WCO issues Area Hydrological Discussion (AHD) at Jul 16, 10:23 AM CDT770
AGUS74 KWCO 161531
AHDNWC
Area Hydrological Discussion #189 - EXPERIMENTAL
NWS National Water Center - Tuscaloosa, AL
1023 AM CDT Tue Jul 16 2024
WHAT: Flash, urban, and small stream flooding.
WHERE: Extreme eastern MO into southern IL
WHEN: Through the late afternoon.
FORECAST RAINFALL AND ANTECEDENT CONDITIONS
QPF: 2 - 5" locally higher amounts (HRRR)
Rates: 1 - 2"/hr (WPC)
Soil Moisture: Dry (30 - 50% RSM, 0 - 10 cm/0 - 100 cm NASA SPoRT)
Streamflows: Normal to much above normal (USGS)
DISCUSSION...
Current heavy rainfall in the area of concern is increasingly posing
the threat for flash, urban, and small stream flooding. Antecedent
conditions are not conducive to flooding-since soils are dry and
streams have the capacity to handle excess runoff-intense forecast
rainfall rates are expected to overwhelm soil capacity, causing
runoff to flow into nearby streams and rivers. There is the
possibility of rainfall stalling or training over some areas, which
could produce locally significant impacts, even if soils are not yet
saturated.
The HRRR-forced National Water Model is increasingly signaling for
rapid on-set flooding (ROF) and small stream responses. A
concentrated cluster of ROF signals is located in extreme eastern MO
extending into southern IL, but probabilities are slow to reflect the
increasing intensity of convection, resulting in lower estimates.
Lower annual exceedance probabilities (AEPs) of less than 2%,
according to the 18-hour Maximum High Flow Magnitude Forecast, are
found west and southeast of St. Louis, with widespread high water
probabilities of 50 - 75%, boosting confidence in small stream
responses throughout the area. These signals combined with the
convective nature of rainfall, indicate that standing water on
roadways, overflowing storm drains and culverts, and flooding of
poorly drained and low-lying areas in urban centers are likely.
GRAPHICAL REPRESENTATION weather.gov/owp/operations-ahd
Additional National Water Center products are available at
weather.gov/owp/operations
//Wood/Whisnant
ATTN...WFO...EAX...SGF...ILX...PAH...LSX...IND
ATTN...RFC...ORN...KRF...MSR...TIR...WPC
Source:
WCO issues Area Hydrological Discussion (AHD) at Jul 16, 10:23 AM CDT---------------
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